This application is being filed concurrently with the following U.S. patent application, the entire disclosure of which is incorporated by reference in its entirety for all purposes:
Suzanne Wakelin, Matthew W. Derstine, and James S. Wong, titled xe2x80x9cMicrolens Array with Spatially Varying Optical Propertyxe2x80x9d U.S. patent application Ser. No. 09/423,293.
The present invention relates generally to optical communications, and more specifically to techniques for coupling light from an array, typically two-dimensional (2D), of optical sources on a chip or board to a corresponding array of optical detectors on another chip or board.
The need for high performance processors with large addressable memory will continue to increase. Continued evolution of digital CMOS technology processors can provide the basis for supporting these requirements; Giga-op (one billion operations per second) single chip processing devices will be available in the near future. However, the electrical interconnect fabric is not scaleable with digital signal processing technology. Conventional, electrical interconnect capacity can only be increased through the use of more wires requiring large devices and boards, and/or higher speed data transfer clocks requiring excessive power.
One approach to overcoming the limitations of conventional electrical interconnections is the uses of optical interconnections (i.e., arrays of photonic transmitters and receivers communicating over an optical backplane). Each electrical signal that is to be sent from a first chip or board to a second chip or board is communicated to an electrical-to-optical conversion (E/O) device (i.e., is used to drive an optical source) on the first chip or board. The light from the optical source is then communicated to an optical-to-electrical conversion (O/E) device (i.e., optical detector) on the second chip or board, which detector provides an electrical signal, which is communicated to appropriate electronic circuitry on the second chip or board.
There are a number of methods and approaches described for connecting 2D arrays of optical elements from one chip or board to another. The basic disadvantage of most of the systems are that they are relatively sensitive to alignment and or environmental changes. In particular, the prior systems used heavy metal baseplates, highly adjustable optical systems, or were designed to be used with precisely aligned monolithic optical systems.
The present invention provides apparatus and methods for efficiently coupling light between arrays of optical sources and detectors. The sources and detectors can be active devices or can be arrays of terminated fiber optic elements. The invention provides optical components that are rugged, low cost, and easily assembled.
An optical system for imaging an array of light sources according to an embodiment of the invention includes an array of microlenses disposed to intercept light from respective light sources in the array of light sources to reduce the divergence angles of light emanating from the light sources, a first array of lenses (sometimes referred to as minilenses), and a second array of lenses (minilenses). Each lens in the first array is sized to intercept light from a respective sub-plurality of the microlenses, and each lens in the second array intercepts and focuses light from a respective lens in the first array. The first and second arrays of minilenses are preferably configured to define a doubly-telecentric imaging system. The doubly-telecentric imaging system may have unit magnification or a magnification other than unity.
A further embodiment of the invention includes an additional array of microlenses disposed to intercept and focus light from the second array of lenses. Each microlens in the additional array intercepts and focuses light that originated from a respective light source in the array of light sources and passed through a respective microlens in the first-mentioned array of microlenses.
The optical system may be used with an array of detectors, each one optically conjugate with a respective light source in the array of light sources. If the detectors are generally commensurate in size with the microlenses in the first mentioned-array of microlenses, the light emerging from the second array of lenses may be directed to the detectors without intervening microlenses. In the event that the detectors are significantly smaller than the microlenses, it may be preferred to use the further embodiment of the optical system, which includes the additional array of microlenses.
In a particular geometric arrangement of the optical system, the array of sources and the array of microlenses are arranged as respective pluralities of separated clusters according to a predefined pattern, and the lenses in the first array are arranged according to the predefined pattern with each lens in the first array having a lateral extent greater than the lateral extent of a respective one of the clusters.
A method of imaging an array of light sources according to an embodiment of the invention includes reducing the divergence angle of light emanating from each of the light sources to provide a corresponding set of less-divergent beams, and for each of a plurality of subsets of beams, using respective first and second lenses to relay and focus that subset of beams. The method may further include increasing the convergence angle of each beam emanating from the second lenses. The method may include using a microlens array to reduce the divergence angle of light emanating from each of the light sources, or to increase the convergence angle of each beam emanating from the second lenses.
A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and the drawings.